Supporters of Mississippi GOP state Sen. Chris McDaniel hoist campaign signs at a rally Oct. 17, 2013. His decision to run will probably pit him against longtime incumbent Republican Sen. Thad Cochran in the primary. / Rogelio V. Solis, AP

by Susan Davis, USA TODAY

by Susan Davis, USA TODAY

WASHINGTON - The 2014 primary election season that kicks off March 4 may serve as a test of the Tea Party's ability to shape the Republican Party.

The movement that became a potent political force in the 2010 elections and helped Republicans retake control of the House is at war with the Republican establishment and taking on GOP incumbents in a handful of key races.

All but one of six Tea Party challenges to Senate Republican incumbents this year are in states where a primary victory is tantamount to a general election victory. In these heavily Republican states - in theory - a Tea Party candidate should have the best opportunity for victory because primaries tend to see lower turnout races populated by the party's base.

"If they (Tea Party candidates) don't do well, if they can't do it in red states against incumbents, then how effective are they really?" said Jennifer Duffy, a non-partisan election analyst for The Cook Political Report. "I think this is going to be a pretty decisive cycle in terms of that question."

The GOP campaign committees, particularly the National Republican Senatorial Committee, have pressed incumbents to prepare themselves for primary opponents while warning outside GOP consultants not to work with challengers. House Speaker John Boehner, R-Ohio, has publicly waged battle with outside conservative groups, such as the Club for Growth, that fuel many of these 2014 incumbent challengers. He accused the groups in December of "using the American people for their own goals."

The establishment has wised up to the threat. "All of our incumbents are coming back," said Rob Collins, executive director of the NRSC. "They have not only built the best campaigns to get out their message, they have raised the resources they need, and their votes and their legislative record reflect the majority of the Republican electorate in their states."

Though anti-incumbent candidates face uphill battles and few advantages in 2014, there is no less enthusiasm this cycle among Tea Party activists and candidates seeking to upend the status quo.

"It's really about establishment incumbents who have been here way too long. They've gotten comfortable with business-as-usual vs. people in America and the candidates that represent them who actually want to come here and do what they said they were going to do," said Matt Kibbe, president of FreedomWorks, a Tea Party group that has endorsed a handful of candidates this cycle.

ADVANTAGE: INCUMBENT

Senate GOP incumbent primaries are playing out in some of the nation's most conservative states: Kansas, Mississippi, South Carolina, Tennessee and Texas.

Texas Republican John Cornyn is poised to easily dispatch his March 4 primary challenger, Rep. Steve Stockman, who never mustered the statewide organization or fundraising to mount a serious challenge. Tennessee's Lamar Alexander is likewise the heavy favorite in his August primary race against state Rep. Joe Carr.

Senate Minority Leader Mitch McConnell of Kentucky is more likely to face trouble from his likely Democratic challenger, Alison Lundergan Grimes, than from his May primary opponent, Matt Bevin. McConnell led Bevin by 26 percentage points in a recent poll.

At a Washington candidate forum hosted by FreedomWorks, Bevin was confident he could close the gap. "I like where we are. It's always good to be the underdog. It's good to be the stealth player under the radar screen," he said. "The reality is, we're closing (the gap)."

TEA PARTY CHALLENGERS

Duffy estimates Mississippi's Thad Cochran, 76, is the most vulnerable Senate Republican, largely because he hasn't faced a tough race since 1984.

"He's been moving away from our conservative base for an awful long time," said Chris McDaniel, a state senator and Cochran's leading opponent. "They're (voters) looking for change, and they sense that change is possible this time, and they're very enthusiastic."

Like Bevin, McDaniel is backed by FreedomWorks and the Club for Growth. Though many primary challengers struggle to raise funds, McDaniel raised nearly half a million dollars in the early weeks of his campaign.

Sen. Pat Roberts of Kansas faces a spirited challenge from Milton Wolf, a distant cousin of President Obama. Roberts may have been weakened by a recent New York Times story indicating that he does not own a home in the state.

Sen. Lindsey Graham of South Carolina has amassed at least five opponents for his contest. Unless Graham can muster 50% in the primary June 10, which is difficult in a crowded field, he will race a one-on-one runoff two weeks later. Runoff primaries can be politically perilous for incumbents because they generally have even lower turnout than primaries.

TEA PARTY TRIO IN THE HOUSE

While the anti-establishment outside groups are focused on the Senate, where control of the chamber is up for grabs, three veteran GOP incumbents in the House â?? Reps. Pete Sessions of Texas, Mike Simpson of Idaho and Bill Shuster of Pennsylvania â?? face high-profile primary challenges.

Simpson has a well-funded challenger, Bryan Smith, who is backed by the Club for Growth.

Sessions faces Katrina Pierson, a Tea Party activist and television commentator who was endorsed by former Alaska governor Sarah Palin. Pierson has failed to raise much money to compete in the Dallas-area media market. Shuster faces a Tea Party-aligned Coast Guard retiree named Art Halvorson, who has failed to raise the kind of money that makes incumbents pause.

Kibbe said the grass-roots movement to reshape the GOP will be won in incremental victories.

"I think they're (establishment candidates) going to have a hard time winning, but it's at the margin," he said, "We have to add more of our candidates to the House and Senate caucus, and over time, we become the new normal."